M20C carburetor adjustment

[Shadrach]

On 3/18/2019 at 5:51 PM, Shiny moose said:

I can understand your point and trying to help this guy figure out a maybe problem, or maybe not a problem, but my point was that he needs a min FF to get the full power On an O360 180 HP  200HP or any other  piston powered engine, more than that will be for cooling, to much and you’ve caused another issue, to less fuel flow than needed to produce the rated power and you will not get to that HP no matter what you do to the engine. The manufacturer gives you what they need for FF for the additional cooling.  In our world  I dont think you can pull more HP out of a .5 pound of fuel than it has in it. If someone said they have an IO360 200HP that they have modified to burn only 10 gph on take off and 5gph per hour at 70% power I would call it a scam. 

An IO360 200HP pushing 60% or 120 HP will burn 10gph or a O360 180HP pushing 67 % or 120HP will burn the same 10gph, or how about a 540 400HP, if it is ran at 30% or 120HP ( dont know why we would do this ) you would burn 10gph. It’s about the HP not the engine size.

I agree BTU is what is what energy it takes to raise one pound of water by 1 degree, and fuel has BTUs , but BFSC is directly realated to this question as it is fuel flow per hour (pounds per hour) divided by HP . 

 

In order to have this conversation, one needs to know how many horsepower a given engine makes on a unit of fuel.  The guys at GAMI and APS have already given us easy multipliers to to derive HP from FF while lean of peak.  Those numbers work as a good approximation for the amount of fuel being used to make power on the the rich side of peak.  They approximate multipliers are as follows 15.13 for an 8.7:1 engine. 14.9 for a 8.5:1 engine. 13.7 for a 7.5:1 engine.  So an O360 making 180HP on a standard day theoretically needs about 12GPH to make 180HP strictly from a BTU standpoint, an IO360 making 200hp needs about 13.2GPH and finally a TSIO360 making 210hp needs about 15.3GPH.  These FF numbers account for power only, not cooling. An engine leaned to those max power numbers would not last long. All of the additional fuel is used for for slowing the combustion event.  We use the term "burning  XXGPH" on take off, but what's really happening is that a significant portion of our take off FF is used to slow the flame front and keep our cylinders from self destructing.  If you look in your POH you will notice a dramatic drop off in FF needed to produce HP at 65%.  That is because the POH allows for lean operation at lower power settings.  I would add that an IO360 will happily make 120HP (60%) on 8GPH.  It will also happily make 160HP (80%) on around 10.5GPH down low.

So to be clear, Dev had or has plenty of fuel to make power. He was concerned he was not getting enough fuel to keep the engine cool.

[Hammbone]

Ahoy DXB. Several items can effect total fuel flow other than the carb. is the throttle against the open stop? Is the mixture against the open stop? Assuming a Vernier control, after it is pushed in. continue to turn clockwise until it stops. are you sure your prop is turning 2700 rpms. Tachs are notoriously inaccurate. A governor adjustment would fix this. These are cheap fixes compared to pulling a carburetor. Finally if you climb at Vy { 100 mph) for more than a minute or two, the back cylinders will overheat. Try 110 to 120 instead. I think you will find your CHT's will run lower and climb rate will suffer only a modest decrease. Hope this helps.

[carusoam]

Welcome aboard, Hamm.

Check the age of the posts here...

It is one of the long running discussions... 

Best regards,

-a-

[Shadrach]

36 minutes ago, Hammbone said:

Ahoy DXB. Several items can effect total fuel flow other than the carb. is the throttle against the open stop? Is the mixture against the open stop? Assuming a Vernier control, after it is pushed in. continue to turn clockwise until it stops. are you sure your prop is turning 2700 rpms. Tachs are notoriously inaccurate. A governor adjustment would fix this. These are cheap fixes compared to pulling a carburetor. Finally if you climb at Vy { 100 mph) for more than a minute or two, the back cylinders will overheat. Try 110 to 120 instead. I think you will find your CHT's will run lower and climb rate will suffer only a modest decrease. Hope this helps.

Is this unique to to parallel valve Lycomings?  The angle valve in my F model does not overheat at Vy even on the hottest days.